A carpenter pencil is usually rectangular in shape, which is intended to stabilize the pencil when placed on a flat or angled surface to prevent it from rolling.
Unfortunately, because of its shape a carpenter pencil is not compatible with a conventional-cylindrical-pencil sharper for sharpening cylindrically shaped, wooden pencils. Specifically, a carpenter pencil is too large for the opening of a pencil sharpener for cylindrically shaped pencils.
There is generally only one category of dedicated-sharpener devices available for sharpening carpenter pencils: manual. These sharpeners are usually inexpensive and portable, but are very slow. For instance, it can take well over one minute to sharpen a carpenter pencil using a manual sharpener on the market today, among other drawbacks.